Pure speculation and rent seeking doesn't really do anything but leach of someone's else effort. Wealth doesn't appear out of thin air, it was created somehow. In the case of Cupertino, Asian immigrants from the 80s as well as the obvious tech scene made it a desirable place to live. Not everyone just bought property and sat on it just waiting for something to happen, people had to actually make it happen.

I guess if you want to make money as a speculator/rent seeker, you look for people doing things to improve and then take a bet that things will get better than other speculators think. But you are relying on other people doing the work for you, which is risky.